DNA passes most genetic information today. But some scientists think that for the first life on Earth, genetic information was passed by RNA. They call this the RNA world hypothesis.

Metabolism

Organic molecules must carry out the chemical work of cells. This is their
metabolism
. Living organisms need chemical reactions to live, grow, and reproduce. The chemical reactions occur in sequences of steps. These sequences are known as metabolic pathways. The metabolic pathways are very similar for all life on Earth. That includes single celled bacteria that have been around for billions of years. It includes the most complex life forms on Earth today. What does it mean that the metabolic pathways are so similar for all life? This means that the metabolic pathways evolved very early in Earth's history.

Replication

Living cells need organic molecules, known as
nucleic acids
. Nucleic acids are molecules that store genetic information. They pass that genetic information to the next generation. Deoxyribonucleic acid (DNA) is the nucleic acid that carries information for nearly all living cells today. DNA has done this for most of Earth's history. Ribonucleic acid (RNA) delivers genetic instructions to the location in a cell where protein is synthesized. RNA regulates protein synthesis. Some scientists think that RNA was the first replicating molecule.

A segment of DNA that is inheritable is a
gene
. Every organism has a collection of genes that code for the traits that organism could have. Not all genes are expressed; therefore, knowing all of your genes does not tell you exactly who you are.

Summary

An organism's metabolism is the chemical reactions that allow it to live, grow, and reproduce.